Liquid crystal displays (LCD) are widely used flat panel displays. The LCDs realizes screen display by switching liquid crystals to adjust backlight field intensity. Organic light emitting diode (OLED) devices have great application prospects in flat panel displays due to advantages of self-emitting, fully solid state, wide view angle, and quick response. The OLED devices are even considered to be a new generation product of flat panel displays following LCDs, and PDPs (plasma display panels).
The LCDs and the OLED display devices both comprise thin film transistor (TFT) devices. In this art, manufacturing process of the thin film transistor generally includes five masks. Production cost and duration will increase because too many masks are required, and production efficiency will greatly lowered. For reducing number of the masks, many companies have developed four-mask technology to form active layer (AS) and source/drain electrode (S/D) at the same time with one halftone mask (HTM) or one gray scale mask (GTM). The HTM or the GTM can form two different thicknesses of the photoresist, and the two thicknesses can define the pattern of the AS and the pattern of the S/D, respectively.
For further reducing the number of the masks, a lift-off process (stripping process) can be used for forming the ITO (transparent metal layer) and the PV (passivation layer) simultaneously with one mask, thereby the total number of masks can be reduced to 3 masks. However, the conventional 3-mask process is usually used for twisted nematic (TN) mode panels having the ITO without slits, or the ITO with slits. The ITO can only be deposited at the openings of the ITO with slits so that all ITO layers (including the pixel area) are in the recesses of the nitrogen silicon compound. The lateral electric field is lowered so as to affect display of the liquid crystal display and form uneven brightness. With development of technology, improved 3-mask technology is provides a PV/ITO layer formed by using a HTM or GTM mask, so that the pixel area of the ITO can form the slit, and cover the PV layer to form the structure the same as that produced by using 4 masks.
It is difficult for this 3-mask process to strip the photoresist which is covered by the ITO so that the stripping and efficiency are poor. In addition, residual photoresist after stripping and burr issues both can seriously affect process or product performance.